XXY111 INTEODUCTION. 



therefore to some extent at home in this new investi- 

 gation. The calamity was appalling, all the efforts 

 made to stay the plague having proved futile. In 

 June 1865 Pasteur betook himself to the scene of the 

 epidemic, and at once commenced his observations. 

 On the evening of his arrival he had already discovered 

 the corpuscles, and shown them to others. Acquainted 

 as he was with the work of living ferments, his mind 

 was prepared to see in the corpuscles the cause of the 

 epidemic. He followed them through all the phases 

 of the insect's life through the eggs, through the 

 worm, through the chrysalis, through the moth. He 

 proved that the germ of the malady might be present 

 in the eggs and escape detection. In the worm also 

 it might elude microscopic examination. But in the 

 moth it reached a development so distinct as to ren- 

 der its recognition immediate. From healthy moths 

 healthy eggs were sure to spring ; from healthy eggs 

 healthy worms ; from healthy worms fine cocoons : so 

 that the problem of the restoration to France of its 

 silk-husbandry reduced itself to the separation of the 

 healthy from the unhealthy moths, the rejection of 

 the latter, and the exclusive employment of the eggs 

 of the former. M. Kadot describes how this is now 

 done on the largest scale, with the most satisfactory 

 results. 



The bearing of this investigation on the parasitic 

 theory of communicable diseases was thus illustrated : 



